[Tex/LaTex] Underfull \hbox (badness 10000) in paragraph in tabularx

tabularx

I know this problem is largely discussed but I tried some solution which did not work; and I saw some post saying that the best for this problem is to share the code because it is very specific so here I am !

As you guessed from the title, when compiling a table I get the error : 

Underfull \hbox (badness 10000) in paragraph

And I don't really know how to solve it. Some post say it comes from the \\but if I delete them, I don't have the underline and the error still occur !

\begin{table}
    \centering
    \begin{tabularx}{\textwidth}{|c|c|X|X|X|X|}
        \hline 
        - & Top gem & A & B & C & D \\ \hline 
        Surface quality & Flawless & 90\% flawless, 10\% light defects and up to 2 defects & 70\% flawless, 30\% light defects and up to 2 deep defects & 40\% flawless, 60\% light defects and up to 10\% deep defects defects & More than 60\% light defects and up to 20\% deep defects defects \\ \hline 
        Lustre & Excellent & Very good at least & Good at least & Medium at least & Low at least \\ \hline 
    \end{tabularx} 
\end{table}

Thanks you for reading ! And have a good day !
PS : I use TeXstudio (If it really matters)

Best Answer

It is caused in this case by the narrow columns, if you set the text ragged right it looks better

\documentclass{article}
\usepackage{tabularx}
\begin{document}

\begin{table}
    \centering
    \begin{tabularx}{\textwidth}{|c|c|>{\raggedright\arraybackslash}X|>{\raggedright\arraybackslash}X|>{\raggedright\arraybackslash}X|>{\raggedright\arraybackslash}X|}
        \hline 
        - & Top gem & A & B & C & D \\ \hline 
        Surface quality & Flawless & 90\% flawless, 10\% light defects and up to 2 defects & 70\% flawless, 30\% light defects and up to 2 deep defects & 40\% flawless, 60\% light defects and up to 10\% deep defects defects & More than 60\% light defects and up to 20\% deep defects defects \\ \hline 
        Lustre & Excellent & Very good at least & Good at least & Medium at least & Low at least \\ \hline 
    \end{tabularx} 
\end{table}
\end{document}

an "underfull hbox" means that the white space in lines has been stretched to much, in this case as you could only get two words on a line in many cases the single space between them was being over-stretched to justify the text, setting it raggedright avoids that.

The relation to mis-use of \\ doesn't apply here. People often put \\ at the end of a paragraph, for technical reasons that then forces a completely empty line after the paragraph which is then stretched to full width and gives the same underfull hbox warning as in your case.

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